Common rail fuel injectors provide a way to introduce fuel into the combustion chamber of an engine. Typical common rail fuel injectors include an actuating solenoid that opens a fuel injector nozzle when the solenoid is energized. Fuel is then injected into the combustion chamber as a function of the time period during which the solenoid remains energized. Accurate control of both the delivery timing and duration of fuel is important to engine performance and emissions.
To optimize engine performance and emissions, engine manufacturers may vary the times when the solenoid is energized and de-energized, as well as the magnitude of the current applied to the solenoid. One such example is described in U.S. Pat. No. 4,922,878 (the '878 patent) issued to Shinogle et al. on May 8, 1990. The '878 patent describes a solenoid control circuit that controls actuation of an injector control valve. The solenoid control circuit provides a three tier current waveform having a pull-in current level, a hold-in current level, and an intermediate current level. Energizing the solenoid at the pull-in level starts movement of the control valve and the flow of fuel to the engine. After the control valve starts to move, the current level is reduced to the intermediate level, which is less than the pull-in current level but great enough to continue movement of the control valve. The applied current is then further reduced to the hold-in level to hold the control valve at the moved position. The solenoid may then be de-energized to return the control valve to its initial position to stop the flow of fuel to the engine.
Although the solenoid control circuit of the '878 patent may sufficiently inject fuel into an engine, it may do little to minimize bouncing of the control valve and the resulting effects. In particular, due to inertia of the moving control valve and the associated fuel, upon fully opening, the control valve may tend to bounce away from an upper seat, thereby adversely affecting fuel delivery characteristics. Because the hold-in current of the '878 patent is single tiered, it may be insufficient to fully minimize control valve bouncing. Alternatively, if the hold-in current of the '878 patent is sufficient to minimize control valve bouncing, it may be inefficient for holding the control valve at the moved position after the tendency to bounce has decreased. In addition, the '878 patent does not adjust the tier levels to accommodate the effects of bouncing between closely coupled injections or dampen the closing movements of the control valve to minimize the likelihood of return bouncing.
The control system of the present disclosure solves one or more of the problems set forth above.